1. Field of the Invention
The present invention generally relates to a voltage generating circuit, and more particularly relates to a voltage generating circuit for generating tri-state output logic by one input control.
2. Description of the Prior Art
In electronic circuits, stable power supply deeply concerns the performance of an electronic device. Unstable power supply may cause operation errors in the electronic device, or further damage the electronic device and decrease its working life. Referring to FIG. 1, the voltage generating circuit 10 provides output voltage 102 to the voltage monitoring circuit 14. Voltage monitoring circuit 14 detects the output voltage 102 and then compares it with a voltage reference 106. When output voltage 102 is smaller than the reference voltage 106, the voltage monitoring circuit 14 generates an alarm signal 108 to processor 12 for triggering the protection mechanism of the processor 12.
Generally, the output voltage 102 of the voltage generating circuit 10 is not fixed but has various selecting voltage levels to fit each kind of applications. An exemplary voltage generating circuit could be a voltage divider, which generates two outputs (with two selecting voltage levels) in accordance with a binary signal inputted via a programmable pin. In other words, one input generates two outputs. Therefore, there are at most 2N combinations of output voltage levels when having N programmable pins for receiving N inputted setting voltages. For another example, U.S. patent application Ser. No. 2004/0085053 “Programmable voltage supervisory circuit and method with minimum programming pins and low quiescent current” discloses a voltage monitoring circuit, herein provides a voltage generating circuit that capable of generating tri-state output logic by one input control.
It's well known that how to decrease power consumption is one important issue to many electronic devices. The voltage monitoring circuit of the aforementioned U.S. patent application utilizes a sample-and-hold method to save power consumption. In order to reduce the whole power consumption of an electronic device (referring to the system shown in the FIG. 1), however, to reduce the power consumption of the voltage generating circuit is the most straightforward. According to this motivation, a voltage generating circuit, which generates tri-state output by one input control and has very low quiescent current, is provided.